1. Field of the Invention
The present invention relates to a gas discharge tube; and, in particular, to a gas discharge tube for use as a light source for a spectroscope, chromatography, or the like.
2. Related Background Art
As techniques in such a field, those disclosed in Japanese Patent Application Laid-Open Nos. HEI 7-326324 and HEI 8-222185 have conventionally been known. In the gas discharge tubes described in these publications, a sealed envelope is constituted by a side tube made of glass and a stem made of glass, stem pins are secured to the stem, anode and cathode sections are secured to the respective stempins, and the sealed envelope is filled with about several Torr of deuterium gas. Such a gas discharge tube is constructed as a deuterium lamp and is utilized as a stable UV light source.
Since the conventional gas discharge tubes are configured as mentioned above, however, there have been problems as follows.
Namely, while the above-mentioned sealed envelope is made of glass as a whole from the viewpoint of freedom in processing, the junction temperature between the side tube made of glass and the stem made of glass exceeds 1000xc2x0 C. when they are thermally fused to each other. As its countermeasures, it is necessary to employ a floating structure in which the anode and cathode sections are spaced from the junction, whereby the sealed envelope increases its dimensions, which inevitably enlarges the gas discharge tube itself.
In order to overcome the problems mentioned above, it is an object of the present invention to provide a gas discharge tube which attains smaller dimensions and freedom in processing at the same time.
For making the gas discharge tube smaller, the inventors have tried experiments using various materials for the stem and side tube. As a result, it has been found that, in the case where the side tube itself is made of a material such as a Kovar metal or the like while a material coated with a glass material or ceramics is used for its wall face, the temperature of the anode and cathode sections rises only about several tens of degrees at the time of joining the sealed envelope thereto, whereby there are no thermal damages to the anode and cathode sections even in a structure in which the side tube is made so small that the cathode and anode sections are disposed closer to the side tube body.
The present invention is achieved according to this finding. Namely, in order to overcome the above-mentioned problems, the gas discharge tube of the present invention is a gas discharge tube having a sealed envelope at least a part of which transmits light, the sealed envelope being filled with a gas and being provided with anode and cathode sections disposed therein, electric discharge being generated between the anode and cathode sections, so that the light-transmitting part of the sealed envelope emits predetermined light outside. The sealed envelope comprises a stem for securing the anode and cathode sections by way of respective stem pins independent from each other a side tube surrounding the anode and cathode sections and being secured to the stem, and a light projection window secured to the side tube and formed from a material transmitting light, wherein the side tube has a wall face coated with a glass material or ceramics.
According to the present invention, the side tube of the gas discharge tube can be formed from a material (e.g., cover metal) other than glass, and there are no thermal damages to the anode and cathode sections at the time of joining the side tube and the stem to each other even in a structure in which the side tube is made so small that the cathode and anode sections are disposed closer to each other, whereby smaller dimensions are easily obtained. Further, since a metal or the like is used as a side tube material, the freedom and stability of processing enhance. Since the tube wall face is coated with a glass material or ceramics, materials which may react with or occlude gases filling the envelope can also be used as a tube material without generating such a reaction or occlusion, whereby it is favorable in that the tube material has a wider selection, lowers the cost, and enhances the easiness in processing.
Preferably, the coating of the wall face of the side tube is crystallized glass. The crystallized glass is glass in which crystals are deposited, so that the crystals and glass are in a mixed state, whereby it is quite favorable as the coating for the side tube.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings. They are given by way of illustration only, and thus should not be considered limitative of the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it is clear that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, and various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.